The objective of this research is to work out the wiring diagram of the oculomotor system. It will be treated as any other control system by being broken down into chains of data processing elements. These hypothetical models are tested (by simulation) to insure that they correctly match available experimental data. These models then form the basis for experiments designed to test specific hypotheses. Five specific projects are proposed. (1) To investigate the theory that the cerebellum is responsible for the adaptation and plasticity observed when the vestibulo-ocular reflex is challenged by sensory-motor rearrangements (e.g. as in wearing reversing prisms). (2) To determine which part of the cerebellum is responsible for improving the performance of the brain stem neural integrator (///dt) which is the major data processing element of the vestibulo-ocular reflex arc. (3) To discover the oculomotor function of the cerebellar vermis (lobes V- VII). (4) To record from the fibers of the medial longitudinal fasciculus to see which neurally coded variables reach oculomotor neurons along this principal pathway. (5) To determine the functional role of en grappe muscle fibers in eye movement control. Most of these projects are possible because we can measure eye movements with great accuracy in chronic animals with a magnetic field method. Total and subtotal cerebellectomies on cats with and without reversing glasses will be used in projects (1) and (2). The vestibulo-ocular reflex gain is accurately measured by rotating cats in darkness with velocity steps. Projects (3) and (4) will use monkeys with lesions or with conventional single unit recording techniques for behaving animals. Project (5) will use Procion dyes and glass pipettes to mark single muscle fibers. Additional projects will be primarily aimed at locating the neural integrator and the saccadic pulse generators more specifically within the brain stem.